Field of the Invention
The present invention relates to a light amount adjusting device that adjusts a light amount by changing an opening diameter of an aperture, a lens barrel mounting the same, and the like.
Description of the Related Art
Optical apparatuses such as interchangeable lenses for a camera may control an opening diameter of an the aperture using a light amount adjusting apparatus arranged in an optical system in order to make the brightness of photographed images appropriate or to vary the depth of field. For example, such a light amount adjusting apparatus may drive aperture blades to change the opening diameter of the aperture by rotating a rotary ring that is provided in the optical path and rotatable about the optical axis, thereby adjusting the light amount passing through the opening of the aperture. Rotary rings driving aperture blades in this way or the like are often rotated by transmitting the driving power of motors or the like via gears. However, the use of a gear mechanism causes backlash or operating noise of gears. Because these have an effect on the accuracy of the control of the opening of the aperture, it is preferable to reduce backlash or operating noise of gears wherever possible. In particular, when the aperture diameter is controlled in response to a variation of the brightness of an object during photographing, drives to both aperture closing direction and aperture opening direction are needed, which cause frequent inversion driving of a motor during photographing, and thereby the backlash increase and operating noise becomes louder.
Japanese Patent Laid-Open No. 2003-121901 discloses a configuration in which an intermediate gear is arranged between the output gear of a motor and a gear of a windmill to be rotated, and the intermediate gear is biased in a predefined direction to suppress the backlash or operating noise of gears. Also, Japanese Patent Laid-Open No. 2009-133440 discloses a configuration in which an elastic gear is provided so as to overlap with a drive ring to be rotated, and the operating noise caused by backlash is reduced by the elastic deformation of the elastic gear.
In the above-mentioned conventional art, as disclosed in Japanese Patent Laid-Open No. 2003-121901 and No. 2009-133440, the rotary ring driving aperture blades is not supported in the center thereof but is engaged with and supported by a plurality of protrusions arranged in its circumference to guide the rotation for the purpose of ease of rotation of the rotary ring. In particular, such a rotary ring is provided with a clearance between the rotary ring and a plurality of protrusions supporting the rotary ring for the purpose of ensuring a certain amount of dimensional tolerance to guarantee that the rotary ring is able to rotate even if a change in dimension due to temperature or humidity, a deformation in setting up or the like may occur. Due to such clearance of the engagement, the center of the rotary ring is more likely to cause eccentric. In addition, the gear mechanism provided for such a rotary ring is configured by engaging a driven gear arranged in the circumference of the rotary ring with a driving gear. Because of this, when the rotary ring is eccentric in the direction in which the driving gear separates from the driven gear on the circumference of the rotary ring, the backlash in engagement become larger. Therefore, the engagement of gears is delayed by that amount, resulting in the occurrence of a delay in change of the opening diameter of the aperture, and thus, the accuracy of the control of the opening diameter of the aperture will be degraded.
However, in Japanese Patent Laid-Open No. 2003-121901 and No. 2009-133440, such delay in the change of the opening diameter of the aperture due to the clearance of the engagement in rotatable support of the rotary ring has not been taken into account. Also, the addition of a configuration to decrease the backlash of gears used in the above-mentioned conventional art may increase drive load and also lead to an increase in the size of the apparatus or an increase in power consumption.